Case sizing for shooting success

During my time as a handloader, I’ve used probably 100 die sets for reloading metallic-cartridges. They were produced by half a dozen different makers, and varied with regard to convenience and precision. But not even the cheapest brand failed to carry out its intended job in a satisfactory manner.

Handloaders sometimes run into trouble with case-sizing operations, but the problem usually stems from the components and/or sloppy die set-up, rather than any flaw in the dies themselves.

You can get into more trouble with a mismanaged sizing-die than just about any other piece of equipment on the reloading bench. Case forming operations are an added complication that merely add to this class of handloading problems. Dies and the sloppy use of them only add to your woes.

With the exception of straight-walled handgun cases sized in a carbide die, adequate lubrication is a necessity. Most reloaders lube the case body, but neglect to lube the inside of case necks. This gives rise to the most frequent difficulty with sizing-dies - excessive drag on the expander button as the case is withdrawn from the die. To know what causes this we need to understand how the die works. Let’s suppose we are resizing a batch of .308 cases.

As the ram of the press forces the case into the die, the case neck is squeezed down to give it a smaller inside diameter less than what is needed to grip the bullet. Then, as the case is pulled back out of the die, the expander button located on the decapping stem is drawn back through the case neck to increase its diameter slightly. On .308 cases, the expander button leaves the necks with an inside diameter of approximately .305-inch. This is the correct dimension to apply .003 to .004-inch of neck tension needed to grasp bullets firmly enough to withstand the forces of cycling through a rifles action and normal recoil.

If the expander button drags and grates as it comes out of the case neck, the handloader may worry about stretching and excessive work hardening. Working case necks overmuch will, of course, make them brittle and cause premature cracking. But can you blame the die? Probably not.

Problems with excessive expander button drag are due to other reasons than any fault in the sizing die. In normal dimension chambers in factory rifles, overthick case necks are rare and the vast majority of times inadequate lubrication is the cause. Insides of case necks should be lightly coated with dry lube. This latter measure reduces drag as the expander button is pulled back through the neck. I used to apply powdered graphite with a case-neck brush, until I discovered it was easier to dip case necks in Redding’s Application Media with Imperial Dry Neck Lube. This is a lot cleaner and lot less messy than graphite.

If the expander button still drags despite being lubricated, then the problem almost certainly lies in the brass. Sad to relate, different lots of brass for the same bottlenecked rifle cartridge can vary from .003 to .004-inch on each side in the thickness of their neck walls. That translates into a total of .006to .008-inch . Repeated firing and necking down to form wildcat cases will thicken necks too. If custom barrels and chambers are used, and particularly if wildcat cartridges are formed by necking down from a larger calibre, or the shoulder set back to form a new neck, the neck may be thickened. When the die sizes the neck down, all of this variation reduces the inside diameter of the case neck. Cases with thick necks, relative to the amount of tolerance allowed by industry specifications, are going to drag on the standard expander button for any given calibre.

Whats’ the solution? The first thing that occurs to the newchum reloader is to reduce the size of the expander button. But this isn’t practical because the resultant inside diameter of case necks will be too tight to easily seat fresh bullets. Forcing bullets into undersized case necks works brass the same as the standard expander button, and can even cause cases to buckle at the shoulder.

To check case thickness and/or wall uniformity, you don’t need to splurge on a special tubing micrometer. Simply take a case with a neck that you know is of the correct thickness, size it down and seat a bullet, then mike it. Then do the same thing with the case you want to check for neck thickness.To determine clearance, measure the neck of a fired case. Rotating the neck of the case case in the mike will indicate whether the thickness of the neck wall is even. Bear in mind, however, that you are measuring average neck thickness and that a thick spot is often balanced by a thin spot on the opposite wall. Be sure that you measure the neck at the same place each time becausenecks are thicker at the shoulder than at the mouth on some cases by as much as .003-inch, but may be the same on others. Short necks normally show less difference than long necks, of course.

Some reloaders believe that repeated firing causes case necks to become thicker; as I did at one time, but after checking this repeatedly with cases of different sizes and calibres, and different length necks, found that it just doesn’t happen. Any brass that is moved forward by repeated firing under high pressure actually lengthens the neck, not thickens it. Even Improved cases with 40-degree shoulders are not immune, and will stretch badly if pressures are high and the brass is soft.

Opening up the neck of the die by, say, .002-inch would get rid of the drag problem, resizing would require less effort and case life would be extended. However, dies are polished and hardened, making this quite a chore. And when your current batch of thick-necked brass wears out and you replace it with a new lot, case necks may be on the thin side. A die modified to suit cases with thick necks won’t reduce thin necks enough to grip bullets securely, and will leave thin-necked cases with a very loose hold on seated bullets.

The only way to correct the problem is inside-reaming or outside-turning the case necks to remove .001-inch or a bit less from case neck circumference. Outside turning is best if you wish to true up the thickness of the neck. This job is rather tedious and must be tackled with extreme care. If you do not already have the necessary reaming or turning tools, it may be less expensive to simply suffer the expander button drag until that lot of cases can be junked. Then, hope that your new lot of brass has thinner neck walls.

Applying too much lube so that it builds up inside the die, or applying it direct to the case shoulder, causes oil dents. These dents look unsightly, but don’t do any harm, and only indicate a sloppy reloading technique. This can be avoided by applying lube to case bodies very sparingly. The lubed case should feel just slightly greasy, without a visible build-up of lubricant. It is not necessary to lube the case neck or shoulder, and of course, it should be kept away from the area around the extractor groove and belt. Periodic cleaning of internal surfaces of dies by spraying them with degreaser and drying them with cotton swabs helps prevent a build up of case lube.

The appearance of a bright ring or a slight crack around the case body just forward of the solid web section gives warning of a possible weakening of the case body at this point. Sometimes the ring is nothing more than a mark made by the sizing die, but don’t take this for granted. Make a feeler by bending a right angle on a piece of thin, stiff wire, then carefully draw it up the inside of the case wall. If it detects a possible depression which it will catch on, this means the case head and body are going to part company on the next firing. Such cases should be junked.

Incipient head separations are either caused by excessive headspace in the rifle or, what is more likely, improper adjustment of the sizing die. In effect, the latter is man-made being established during the sizing operation.

When a new unfired case, assuming the brass and chamber conform to industry specifications, initial firing expands the case to fit the chamber. The amount of stretching required to do this isn’t enough to set up incipient head separation.

The problem is commonly caused when the case is resized.

Sizing dies are necessarily dimensioned to produce cases that will fit minimum chambers, but it is impossible to make them. Correctly headspace for all chambers. If the chamber is close to maximum in its head-to-shoulder measurement, setting the die down tight on the shellholder, and then turning it down just a bit more to compensate for any spring in the press might set the shoulder back too far for your particular chamber and cause excessive headspace that will lead to an eventual head separation. When the reloaded cartridge is fired, the case is again fire-formed. Again, it stretches. But it won’t come apart except in the most extreme condition. It merely stretches enough to create a shiny ring and seriously weaken the case. But the case may crack or separate, on the very next firing.

This kind of damage occurs with brass of all types, but is most likely to happen with rimmed and belted cases. As they aren’t intended to headspace on their shoulders, the ammunition makers don’t go to a lot of trouble to precisely locate the shoulder. In a similar manner, when riflemakers cut chambers for such cartridges, the head-to-shoulder dimension is not held to such close tolerances as they apply to chambers for rimless cartridges. As a result case life with rimmed and belted rounds is notoriously short.

Another option is a special tool, like the RCBS Precision Mic, which will measure the actual head-to-shoulder dimension a fire-formed case to within .002-inch. The sizing die can be adjusted accordingly.

Some reloaders feel that by neck resizing cases only, they will last much longer than if full-length resized each time. My experience has not shown this to be true. I’ve found that carrying out full-length resizing or neck resizing makes no difference to the number of reloads you can obtain from a case before the neck splits.

Also, when reloading a modern cartridge in a strong front- locking bolt-action, the majority of those loads will develop higher pressures than factory ammunition. Working at this level, only rarely can a case be reloaded more than two or three times, if neck-sized only, before the body expands to the point where it will not spring back enough to enter the chamber easily. The only way to eliminate this problem is by full-length resizing the sticky cases, so it makes more sense to full-length resize very time in order to ensure reliable functioning.

Those who argue in favour of neck resizing claim that accuracy is enhanced because the case body remains a perfect fit in the chamber, which consequently positions the bullet in perfect alignment with the bore. In reality, because the die is made large enough to fit over the case body, it is not held rigidly, and being such a loose fit the case body is free to move in any direction away from centre, and true bullet/case alignment is not always achieved. Too, if the case neck is thicker on one side the bullet may be forced toward the thin side and out of line. Furthermore, if the rifle chamber is not fully concentric, the bullet may not align perfectly with the bore even if it is in alignment with the case body. As bullet/bore alignment is absolutely essential to fine accuracy, there is no real advantage to be gained by neck sizing only, at least where hunting rifles are concerned. The only exception is the method used by benchrest shooters, which is an entirely different technique.

One minor advantage of neck resizing only is that cases tend to stretch less and require trimming less often. But this is of no great importance because cases have to be trimmed back to minimum length periodically anyway.

Many reloaders attempt to prolong case life by “partially” resizing their brass in full-length dies. This is done by backing the die off so as to adequately resize the case neck, while leaving the body more or less as it was fire-formed. But this doesn’t always work.

Partial resizing works quite well with some case designs, but not so well with others. Cases having plenty of body taper - like the .22-250 for example - generally respond reasonably well to this treatment. But if the chamber happens to have minimum dimensions, the body may not be sized down enough to enter the chamber freely if the case has been fired at high pressures. As the bolt handle is turned down, it abruptly stops as if the cartridge is too long for the chamber, which it is.

You can back the sizing die a full turn away from the shell holder, which with standard 7/8x14 die threads allows about .070- inch of travel, and basically does away with resizing pressure on the case body. Cases with very little body taper, such as the .243 and .308 Winchester, the “improved” wildcats and Short Magnums, behave entirely differently. If the die is screwed down far enough to effectively resize the case neck, it also resizes the body. The shoulder, however, is unsupported. And this, in turn, is a bad thing.

Attempting to partially resize a minimum taper case is rather like squeezing toothpaste out of a tube. What happens is that in partially resizing the case until the body is reduced enough to allow it to enter the chamber, the brass is squeezed down. Not all of this brass returns to its original form and thickness, some of it moves forward slightly, and as the shoulder of the case is receiving no support from the die, as it would be if set for the correct headspace, when the diameter is reduced, the shoulder moves foreward slightly.

If the die is not turned down far enough to support the shoulder, the head-to-shoulder dimension may increase .005-inch, or even as much as .010-inch in some instances. Remember that the case expands to become a tight fit in the chamber on firing, and can be readily extracted only because the brass has enough elasticity to allow it to spring away from the chamber walls. Obviously then, even as little as .001-inch of forward movement of the shoulder will be too much to allow the round to fully chamber.

Gaining the correct headspacing of a cartridge for the chamber in your rifle and eliminate chambering problems associated with partial resizing, is easy if you follow the this procedure: screw the die down until it touches the shell holder with the ram fully raised, then back it off about one-half turn. Size the case and try
to chamber it in the rifle. If it will not go in, or chambers only with difficulty, set the die down about 1/8 turn and repeat. Just continue to size and try until the case chambers with just a slight “feel” when the bolt is fully closed. The die is now correctly set for the longest possible case life without any risk of a head separation. This slight crush fit is ideal for target/varmint cartridges, but for big-game hunting it is a good idea to set the die down another 1/16 turn to allow the cartridge to chamber easily, but still producing a head-to-shoulder fit close enough to avoid a head separation.

When headspace problems crop up with any type of case - rimless, belted or rimmed - the reloader straightaway places blame on the die, but only rarely is it at fault. About 99- percent of the time, it is the rifle chamber and/or the cartridge case that is the cause, aided and abetted by a sloppy reloading technique. Most of the difficulties we meet in handloading are largely of our own making. Fortunately these troubles can be eliminated or avoided rather easily. Regardless of the head style of the case, it is vital to ensure the head-to-shoulder fit in the chamber is snug, but not tight enough to cause a chambering problem in the field.

This article was first published in Sporting Shooter, May 2011.

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